This is less of a 'Bug' and more of a QoL Issue.
When I run in WvW, having the warclaw unlocked, this mount is autoselected as the 'default' for the mount hotkey. However, once I move back to PvE Mode, the warclaw STAYS selected as the default mount. Thus, I have to manually reselect my preferred mount.
The switch of specialization/traits/utility slots works fine, but the 'Mount' slot should really be split between modes, too, so that the warclaw isn't sticking when moving out of WvW again.
Mentioning THAT, Ranger Pets should, if possible, also be 'split' for PvP/PvE/WvW modes, because you otherwise might actually forget to swap back and forth.